How can I make tight clothes that squeezes the body?
ok, lets imagine you want to make a tight boot.

cover the leg with a cube. use some loopcut and slide to give it a siluette of the boot. now use a boolean modifier at the cube - operation intersect and chose the skin of your char as object. 
this will cut away anything from your simplyfied boot that doesnt look like a leg for example, but you will not have a closed surface.

after that, you put a shrinkwrap modifier on the boot. this will lift the surface of the boot above the  skin. target is skin, mode nearest surface and keep above surface yes. this is important! now, here is a little trick. with offset you tell, how far the surface is away from the leg. 0.01 does a pretty good job, but the trick is even though only two digits behind the  point are shown, values like 0.005 and 0.001 can be used which makes it realy tight.. now you only need a shapekey at the leg and tada. job done.

there are two problems.
1. i am not sure if you can use uv maps
2. whenever another part of your skin passes the area of the boot, it will be covered by the boot two. maybe you can solve this when you first copy and aply the boolean and than cop and aply the shrinkwrap with an offset of .03 or .04. this creates a tighter boot than your simplyfied version. parent it on the armature of your char if you want to move the legs and than let the copy of the boolean and the shrinkwrap do the job. 

play around a little. first the boolean than the shrinkwrap.